1. Field of the Invention
The present invention relates to a charged particle radiation apparatus and, more specifically, to a charged particle radiation apparatus having a beam irradiation condition determination device that determines beam irradiation conditions for charging a sample.
2. Description of the Related Art
In recent years, a wide variety of patterns are used for semiconductor wafers and other samples as semiconductor elements are increasingly highly integrated and miniaturized. In addition, the importance of semiconductor element measurement and inspection is increasing as the semiconductor elements are increasingly highly integrated and miniaturized. Further, as the semiconductor elements are increasingly highly integrated and miniaturized, contact holes performing a function of establishing an electrical connection between multiple layers and grooves formed between line patterns are increasing in depth. The contact holes, in particular, are formed to a considerable depth with their diameter decreased. The aspect ratio (the ratio between the depth and diameter) of some contact holes is higher than 50.
A preliminary charging method (hereinafter may be referred to as the pre-dose method) is known as a method of measuring and inspecting the bottom of such deep holes and deep grooves. The pre-dose method, which is disclosed, for instance, in Japanese Patent No. 4093662 (U.S. Pat. No. 7,977,632), is a method of positively charging a beam irradiation region by irradiating a sample with a beam having a secondary electron emission efficiency (electrons emitted from a sample/electrons incident on the sample) of higher than 1 before beam irradiation for measurement or inspection. Electrons emitted from the bottom due to positive charging are directed toward the surface of the sample without colliding with the sidewall of a deep hole. Therefore, the electrons emitted from the bottom of the hole can be detected with high efficiency.
If the surface of the sample is excessively charged, the potential difference of one region from another region having a different potential may increase to cause electrostatic breakdown. Japanese Patent No. 5117080 (U.S. Pat. No. 8,384,030) describes a preliminary charging condition determination method. This method performs pre-dosing and observation while changing the location of irradiation. When the luminance value of the bottom of a hole pattern increases above a setting, this method concludes that electrostatic breakdown may occur, and then decreases, for instance, a beam acceleration voltage for the purpose of reducing the effect of surface charging.
A method disclosed in Patent WO 2013/011792 A1 acquires images while changing beam conditions and analyzes the acquired images in order to determine pre-dose conditions under which the luminance value difference between an edge peak and a hole bottom is within a predetermined range.